Control of player streams server side

Searching the forums I have seen several topics on this over the years but all seem to suggest remote procedure calls something like,

admin -> server -> client(send play.pause.etc) -> server -> client

for controlling the connected streams.

We have several remote sites with large displays that are unmanned. Once a stream is established by the player (handled in other logic) we would like to control the streams going to these screens remotely, ie be able to play,pause etc. Using a remote call as previously suggested in some forum questions is not ideal for us as the players are custom built and do not have this easily available.

admin(send play.pause.etc) -> server -> client

is there a method to control a stream (once a uuid is identified) serverside? I may have have missed something basic in the manual or the correct terminaolgy but any advice pointing in the right direction would be appreciated.